Continuous culturing device

ABSTRACT

A continuous device for culturing mammalian cells in a three-dimensional structure for the transplantation or implantation in vivo is described. The culturing device comprises (a) a scaffold formed by a matrix of interconnected growth surfaces spaced at regular intervals and (b) a fluid distribution means at the inlet and the exit of the growth areas. The device is particularly useful for culturing bone cells for dental implants or bone reconstruction.

This application is a continuation of U.S. application Ser. No.13/515,685, filed on Oct. 23, 2012, which is a U.S. National Stage ofPCT/EP2010/069768 filed on Dec. 15, 2010, which claims priority to andthe benefit of European Application No. 09179465.1 filed on Dec. 16,2009. The contents of each of which are incorporated herein by referencein their entirety.

The present invention relates to a device for culturing mammalian cellsin a three-dimensional structure for the transplantation or implantationin vivo. More particularly, the present invention relates to acontinuous culturing device for culturing bone cells for dental implantsor bone reconstruction.

There is increasing interest in growing cells in three-dimensional (3D)environments such as on a 3D structure or scaffold. Cell culture on 3Dscaffolds is useful in tissue engineering for the generation ofimplantable tissue structures. Intrinsic difficulties with 3D culturesin 3D scaffolds are (i) the uniform and efficient seeding of cellsthroughout the scaffold pores, and (ii) limited mass transfer to thecells in the central scaffold part.

The past three decades have shown great advances in the area of tissueengineering but the problem associated with the difficulty of culturingcells at the center of deep or thick structures remains.

U.S. Pat. No. 6,194,210 describes a process for hepatitis A virus in anaggregated microcarrier-cell culture.

U.S. Pat. No. 6,218,182 describes a method for culturing 3D tissues, inparticular liver tissue for use as an extracorporeal liver assistdevice, in a bioreactor where cells are seeded and provided with twomedia flows, each contacting a different side of the cells.

US 2009/0186412 describes a porous cell scaffold and methods for itsproduction. All prior art references address the problems that arisewhen a culture system with a high density of cells encounters flowirregularities.

Known bioreactors do not efficiently simulate in vivo nutrient mechanismin thick structures or when culture density is high.

Regulation of flow, delivery of nutrients, gasses and removal of wastein the bodies of mammals is an automated process that encompasses manycomplex functions in the body. Blood is a complex system, that supportsthe ability to transport large quantities of gasses and nutrients to andfrom cells throughout the body. Flow is managed by a complex system thatautomatically alters volume and pressure to redistribute the flow ofblood to areas of high demand. The distribution system includesthousands of branches and each branch may have smaller internaldiameters until finally arriving at the dimensional level where thecells are nourished. The use of Computational Fluid Dynamics (CFD)software permits analysis of the flow within a complex structure and itscontainer. When a suitable combination of characteristics areidentified, the metabolic parameters can be studied to assure that boththe utilisation rate of materials and the production of waste productsremain in a typically safe zone. One example would be to calculate themaximum cell density and the oxygen consumption rate, to assure that allthe cells remain aerobic.

We have now found a continuous culture device which solves the problemof culturing cells at the center of deep or thick structures.

Object of the present invention is a continuous culture devicecomprising (a) a scaffold formed by a matrix of interconnected growthsurfaces spaced at regular intervals and (b) a fluid distribution meansat the inlet and the exit of the growth areas.

The spacing and definition are arranged to permit directional flowthrough and around the growth surfaces uniformly.

The fluid distribution means at the inlet and the exit of the growthareas permits an adequate flow to each growth surfaces. The fluiddistribution is analysed using computational fluid dynamics and keymetabolite utilisation analysis to assure that the cells are not subjectto detrimental growth conditions.

Preferably, the fluid distribution means distributes the incoming flowof fresh nutrients and gasses to the growth surfaces. Thecross-sectional area of the distribution device channels and the numberof channels can be adjusted to facilitate the uniform distribution tothe growth surfaces, depending on the shape of the growth surfaces andthe total number of cells supported by the growth surfaces.

Preferably, the culture device includes a matrix of interconnectedgrowth surfaces, defined by the interconnection of multiple fibers orthree-dimensional structures, in an organized and repetitive manner,which can incorporate any number of facets or surface artefacts utilisedto encourage or enhance the attachment and growth of cells.

The three-dimensional structures forming the matrix can be cylindrical,rectangular, hexagonal or any other shape or combination of shapes andthe surfaces may be smooth or textured.

In a practical preferred embodiment of the invention, the scaffold isformed by a matrix of interconnected growth surfaces spaced at regularintervals around a central support.

The open spaces formed by the interconnection of the structures, areequal or larger than 0.7 mm and smaller than 3 mm, preferably equal orlarger than 0.9 mm and smaller than 3 mm. The spacing in the preferredembodiment is greater than 1.0 mm, but can be altered as required by theneed for physical strength of the scaffold. In a still more preferredembodiment of the present invention, the interconnected growth surfacesare spaced at regular intervals equal or larger than 1.0 mm and lessthan 2.0 mm.

Spacing is a characterizing feature of the present invention. Thevariability of the parameter around the above range allows to optimizethe flow of medium throughout the scaffold and, at the same time, toimpart an adequate solidity to the 3D structure for all the devicesaccording to the invention independently from their final shape anddimension. The open spaces formed by the interconnecttion of the growthsurfaces create the organised characterizing structure of the device ofthe present invention which differs from the porous structure of thedevice known from the prior art.

The shape of the scaffold is preferably cubic but it could be anothershape, for example cylindrical or anatomically correct.

Preferably, the culture device includes a large number of interconnectedgrowth surfaces uniformly arranged to create large open areas that limitthe maximum number of cells per cubic volume facilitating the easyvascularization of the growth areas.

The culture device can be made of any biocompatible material.

Biocompatible materials are any biocompatible organic polymer or mixturethereof as well as blends or mixtures of biocompatible organic polymerswith biocompatible organic or inorganic non-polymeric compounds.

Non imitative specific examples of components of the biocompatiblematerial useful in the present invention are polycaprolacton,polyethylene oxide—terephthalate, polyamide, poly-L-lactic acid,polyglycolic acid, collagen, fibronectin, hydroxyapatite, etc.

In a practical preferred embodiment, the culture device furthercomprises an aseptically sealed housing that can be disassembled at thecompletion of the culture period. Said aseptic housing can include asealed removable cover, an inlet distribution means, an optional exitdistribution means, and the necessary support means required to locateand secure the growth surfaces in the culture device.

The housing can be in the form of a rectangle, cylinder or any othershape necessary to hold the culture device and provide additionalfeatures for aseptic removal of the scaffold.

The present invention offers several advantages over previous culturedevices in that nutrient delivery permits the creation of andmaintaining the viability of tissue on a thick (>1 mm) substrate.

The 3D culture device of the present invention can be produced in asingle step process.

Alternatively, a 2D layer can be produced first, and then the single 2Dlayers can be assembled one over the others to form the 3D culturedevice according to the present invention.

The final dimension of the 3D culture device will depend on the numberof assembled 2D layers.

The culture device of the present invention can be efficiently used forculturing any kind of cells into a 3D tissue. Preferably it is used forculturing cells for dental implants or bone reconstruction. Once thecells have grown into a 3D tissue, the media flow may be stopped and thetissue can be used or preserved for future use. The culture device ofthe present invention can be efficiently used also for culturing cellsdirectly into the body. In fact, the device can be implanted into thepatient in need of tissue reconstruction and the culturing is effectedin vivo.

By using the culture device according to the present invention cells maybe grown in a controlled environment on a biodegradable scaffold. Thelarge open areas formed by the interconnection of the growth surfacesallows them to be exposed to a uniform flow of medium and to preventfouling during the growth process. In particular, fouling or blockade ofthe growth surface by gas bubbles during the growth process isprevented.

Moreover, with the culture device of the invention, culture conditionsare monitored continuously and any departures from the desiredconditions are automatically corrected and alarmed. This providesconditions necessary to maintain cells in their undifferentiated state,to minimise the maximum cell density and the associated toxic necrosis,and to provide an environment that is not diffusion limited for keynutrients and gasses.

Furthermore the culture device according to the present inventionprovides the growth of tissues also in the absence of cells, as shown inexperiments carried out on rabbits.

EXAMPLE

Experimental Protocol

A two-layer scaffold (11 mm×11 mm×5 mm) according to the presentinvention, cut in four pieces of equal dimension, was used for the cellgrowth experiment on mice.

Histological Analysis and Results

The four continuous culturing devices were implantated intoimmunodeficient NOD/SCID mice.

The analysis of the inflammatory reaction after one week from theimplantation showed no sign of typical inflammatory reaction, i.e.swelling, redness, exudates, etc.

Histological analysis of the control material HA (Hydroxy Apatite), i.e.a biomedical material commercially available used as standard sample,did not reveal phlogosis (e.g. lymphocytic infiltration) conversely itrevealed the integration of the porous ceramic material with the tissues(fibroblast colonization of the material's pores).

Poly-capro-lactone was removed from all the samples containing thecontinuous culturing device object of the present invention and wasreplaced by paraffin. It resulted in a negative or empty image onmicrophotographs.

Histological analysis of the samples P (Polycaprolactone), PC(Polycaprolactone with cells), PD (Polycaprolactone with tri-calciumphosphate dipping) (FIG. 7), and

PDC (Polycaprolactone with tri-calcium phosphate dipping with cells)(FIG. 8) did not reveal any tissue's inflammatory process. Then theimplantation in vivo of the continuous culturing device object of thepresent invention, provided cell growth without involving tissue'sinflammation process.

The analysis carried out on mice demonstrated that the continuousculturing device is biocompatible and not locally toxic. Moreover thecharacteristic 3D structure of the continuous culturing device providesthe tissue's regrowth.

The present invention is now illustrated in more details in thefollowing drawings which represent specific embodiments of the inventionwithout limiting it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 One embodiment of the scaffold

FIG. 2 One embodiment of a flow distribution device

FIG. 3 One embodiment of scaffold between two flow distribution devices

FIG. 4 System flow chart

FIG. 5 CFD Flow analysis

FIG. 6 Photographic Flow analysis

FIG. 7 Microphotograph of the sample PD

FIG. 8 Microphotograph of the sample PDC

FIG. 9 Photographs of samples HA, PD and PDC

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is one embodiment of the scaffold. Scaffold (1) is formed by theinterconnection of a matrix of cylindrical (3) structures. The scaffold(1) is formed around the central support (2).

FIG. 2 is one embodiment of the fluid distribution device (5). In thisdevice, the fluid is presented to the device (5) at a common conduit (6)which is connected to the distribution conduits (7). A support means (8)is shown to connect with the central support (2) of the scaffold (1).

FIG. 3 depicts a scaffold (1) positioned between two of the distributiondevices (5). In this embodiment the fluid is delivered to the inletcommon conduit (6) and further distribute to distribution conduits (7)and then is distributed through and around the open structures (4) ofscaffold (1). The fluid is then collected and presented to commonconduits (7), located in the outlet device (5B) where it is collectedand presented to the common conduit (6) of the distribution device (5B).

FIG. 4 is an outline view of the culture device (10) connected to acentral circulation system (9). When the culture device (10) isconnected to system (9), it is positioned to receive a continuous flowof nutrients and dissolved gasses provided by pump (12). A centralcirculation loop is created by connecting the outlet of pump (12) withthe inlet of the culture device (10). The outlet of the culture device(10) is connected with the inlet of pump (12) through the fluidreservoir (13). In constant communication with the fluid in the system(12) are a variety of sensors (11). The sensors (11) are connected witha control means (20) that monitors and controls the conditions of system(12). Additional pumps (14, 15) are provided to supply metered deliveryof fresh nutrients to the system, and waste materials from the system.

FIG. 5 illustrates an example of Computational Fluid Dynamics analysis,where the distribution of flow is throughout the structure.

FIG. 6 is a photographic flow analysis.

FIG. 7 and FIG. 8 illustrate the growth of cells and the absence ofinflammatory process for the sample PD and the sample PDC respectively.Microphotographs are 20× of magnification and the cutis are on the topof the microphotographs.

FIG. 9 illustrates the areas of application and analysis of the samplesHA, PD and PDC for the cells growth experiments on mice. The externalanalysis of the samples does not reveal any fibrotic reaction orinflammation process.

The invention claimed is:
 1. A lattice-shaped scaffold for the growth oftissue in vivo, the lattice-shaped scaffold comprising a unitary3-dimensional matrix having x, y and z Cartesian axes withinterconnected growth surfaces spaced at regular intervals in the x, y,z Cartesian axes thereby forming a regular orthogonal 3-dimensionalarrangement of interconnected, cubic open spaces disposed between theinterconnected growth surfaces, where the interconnected, cubic openspaces are along and parallel to the x, y, and z Cartesian axes of thelattice-shaped scaffold, and wherein the regular intervals are equal orlarger than 0.7 mm and smaller than 3.0 mm, and wherein all of theinterconnected growth surfaces are aligned with each other in relationto the x, y and z Cartesian axes.
 2. A scaffold according to claim 1wherein the matrix of interconnected growth surfaces spaced at regularintervals are formed around a central support.
 3. A scaffold accordingto claim 1 wherein the interconnected growth surfaces are defined by theinterconnection of multiple fibers or three-dimensional structures.
 4. Ascaffold according to claim 1 wherein the interconnected growth surfacesare spaced at regular intervals equal or larger than 0.9 mm and smallerthan 3.0 mm.
 5. A scaffold according to claim 1 wherein theinterconnected growth surfaces are spaced at regular intervals equal orlarger than 1.0 mm and smaller than 3.0 mm.
 6. A scaffold according toclaim 1 wherein the interconnected growth surfaces are spaced at regularintervals equal or larger than 1.0 mm and smaller than 2.0 mm.
 7. Amethod of reconstructing tissue in a patient comprising implanting ascaffold of claim 1 into a patient in need thereof.
 8. A scaffoldaccording to claim 2, wherein the central support includes a firstcylindrical support on a first side of the scaffold and a secondcylindrical support on a second side of the scaffold.
 9. A scaffoldaccording to claim 8, wherein the first cylindrical support and thesecond cylindrical support are at oppositely disposed ends of thecentral support.
 10. A scaffold according to claim 1, wherein theinterconnected, cubic open spaces have a substantially equal size.